1. Field of the Invention
The present invention generally relates to electrical resistors fabricated in very large scale integrated (VLSI) analog circuits and, more particularly, to a low-noise ohmic buried resistor fabricated using complementary metal oxide semiconductor (CMOS) technology.
2. Background Description
The buried resistor is a standard element in complementary metal oxide semiconductor (CMOS) technologies. It consists, for example, of an N+ doped region in a P-type substrate (or P-well) and, as such, is strongly coupled to any noise present in the substrate. This prohibits use of the resistor in applications requiring low noise elements, such as analog circuits.
Another type of resistor used in certain types of integrated circuit (IC) technologies is a polysilicon on thick oxide structure that provides lower capacitance to the substrate and thus better noise immunity. These resistors can also be built over an N-well in order to use the N-well as a field shield to further reduce noise coupling to the substrate. However, this type of resistor is not generally compatible with certain CMOS technologies. Furthermore, the buried resistor has much greater heat dissipation capability and is less expensive to manufacture, thus generally more desirable for many applications apart from its poor noise isolation characteristics.